First, it is a given that koshi waza depends on balance, posture, pressure reaction, etc. This forum is about hip motion channeling power into hand and foot technique for explosive focus.
I think the traditional terms and ideas are flawed... not the technique but the way we talk about it. We speak of hip "rotation," hip "vibration" and "pendulum action" as if they were three different things, and I think this confuses students. It certainly confused me for about two decades.
So I propose a more generic definition of koshi waza:
- The hip on the power side (same side as the technique) is the “power hip”. To throw the technique, the performer drives the power hip sharply in the same direction as the technique, which in most cases is straight forward. (Sometimes the power hip generates force upward, or sideways, or to the rear, or even downward, depending on the technique.)
The hip on the opposite side is the "supporting hip." The performer should think of this hip as remaining stationary, to serve as a fulcrum for the power hip.
I have recently had very good results teaching koshi waza in Bassai Dai using this explanation.
Warning: It is a very bad idea to mention “hip rotation” to students. Hip rotation is the outer visual impression one gets watching a person do koshi waza. It isn’t what is happening inside. "Rotation" is a very misleading idea.
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Shihan Randhir Bains once put my class through a koshi waza drill that taught my students isolated control over one hip at a time. Standing in natural stance, arms relaxed, Bains had us drive the right hip forward hard (as if punching) and stop. Then snap the hip back to the neutral position. Repeat several times.
Then the same drill with the left hip. Drive the hip forward hard, all by itself, and snap back to neutral position each time.
Then he surprised us by reversing the motion. Take your right hip and drive it powerfully backward, straight to the rear. Snap back to neutral and repeat. Switch to left hip; drive backward hard and return to neutral.
Bains’s final step was to connect the pieces by having the right hip drive forward AND the left hip drive backward at the same time. Then reverse it, left hip driving forward and right hip driving back. Voila, “hip rotation.”
I have developed a less thorough but more practical variation of this lesson. Last evening I was trying to teach hip technique to a brown belt who just wasn’t getting it. He seemed baffled by the idea until I stood close behind him and knocked him out of stance by slamming my right hip into his butt.
Once he had the idea, I had him stand in natural stance, hands down, and drive the left hip forward and focus, then snap back to neutral position. We repeated this maybe twenty times until he caught on. Then the right hip; drive forward hard and focus, then snap back and try again.
Then left inside block, concentrating on driving the left hip forward hard and focused beneath the blocking elbow... driving forward power into the block. I made him overcome resistance to the block by pushing forward, not sideways. We kept going until he got the hip/arm timing right and could put forward drive behind the block.
Then the right side, same thing. Drive right hip forward under the inside block. Repeat until concept understood, if not mastered.
OK, now, set up for left inside block. On the count, do the left inside block with hip action, then flow directly into the right inside block with hip action.
You should have seen him. The light dawned and the kid did the prettiest and most powerful “hip rotation” you ever saw. Then I taught him the first few inside-block clusters of Bassai Dai and he looked great.
I never mentioned anything about hips “rotating” or a hip going “backward.” All he needed was an awareness of what the power hip had to do, and the rest took care of itself.
